1. Field of the Invention
This invention generally pertains to a bulldozer blade for an earthmoving vehicle, and more particularly, to a two-way bulldozer mechanism which is movable between a pushing mode and a pulling mode to permit bulldozing in both the forward and rearward directions of movement of the vehicle.
2. Description of the Prior Art
Two different prior art two-way bulldozer blade mechanisms which assume two operational modes are individually shown in FIGS. 1 and 2. For simplicity, only one side is shown and described in the following brief description of each mechanism.
FIG. 1 shows a two-way bulldozer blade mechanism which includes upper and lower blade portions hinged together by a hinge pin 7. The lower blade portion is pivotally connected to a push arm 4 by a pin 1 located below the hinge pin 7. The lower blade is provided with an upwardly extending lever arm portion for connecting such blade portion to a piston rod of an oil pressure cylinder 5 by means of a pin 2 located above the hinge pin 7. An upper brace 6 has one end thereof pivotally connected by a pin 8 to a bracket provided on a cross member between the push arms 4 and its other end pivotally connected by a pin 3 to the mid portion of the upper blade portion.
As a result, the upper and lower blade portions assume a pushing mode, as shown in solid lines in FIG. 1, when the piston rod of the cylinder 5 is retracted and a pulling mode, as shown in phantom lines, when the cylinder is extended. The mechanism of FIG. 1 advantageously allows the cutting angle of the lower blade and the curvatures of the moldboards of the blades to be set at desired values, as required. However, since the pin 1 is located substantially below the hinge pin 7, there results an insufficient elevational distance between the tip edge of the lower blade and the forward end of the push arm 4 so that in the pulling mode, the build up of material interfers with the push arm. This makes blade trimming difficult and hinders the piercing action of the lower blade.
FIG. 2 shows another two-way bulldozer blade mechanism wherein components thereof which are similar to those described in FIG. 1 are depicted by like numerals followed by a prime. In FIG. 2, the upper blade is pivotally connected to a push arm 4' at a pivot connection 1' at the center of the upper blade. A brace 6' has one end pivotally connected at 3' to the center of the lower blade portion and its other end pivotally connected at 8' to the under surface of the push arm 4'. The piston rod of a cylinder 5' is pivotally connected at 2' to the upper end of the upper blade. When the cylinder is retracted, the blades assume a pulling mode, as shown in the solid lines of FIG. 2, while when the cylinder is extended, the blades assume a pushing mode, as shown by the phantom lines. Thus, the arrangement of FIG. 2 is similar to an inversion of that of FIG. 1. The most outstanding feature of the mechanism of FIG. 2 is the increased distance provided thereby between the push arm 4' and the ground line which is achieved by positioning the pivot connection 1' above the hinge pin 7'. Thus, there is less interference between the push arm and the material to be removed by the blade mechanism in the pulling mode which reduces blade cutting edge piercing resistance and facilitates the trimming of the bulldozer blade.
However, many problems arise from the particular cutting angle of the lower blade, the curvatures of the moldboards, and the transmission of dozing forces through the mechanism of FIG. 2 to its push arms. In order to achieve maximum bulldozing efficiency, it is necessary that the upper and lower blades assume particular positions to provide a blade cutting angle and a material holding angle which fall within predetermined ranges. In this regard, the blade cutting angle is defined as the inclination of the lower blade to a vertical line normal to the surface of the ground which is designated by the Greek letter .alpha. in FIG. 3A, while the material holding angle is defined as the angle formed between a line connecting the tips of the upper and lower blade and such vertical line which is designated by the Greek letter .beta.. The ideal range for the blade cutting angle is generally between 35.degree. and 38.degree., while the range of the material holding angle is generally between 8.degree. and 13.degree..
FIG. 3A is a diagrammatical illustration of the blade mechanism of FIG. 1 which provides a blade cutting angle .alpha. and a material holding angle .beta. which are within such ideal ranges, while FIG. 3B is illustrative of the blade mechanism of FIG. 2 and shows a cutting angle .alpha.' which is approximately one-half of the desired cutting angle of FIG. 3A and a material holding angle .beta.' which is inclined in a direction opposite to that shown in FIG. 3A.
Consequently, the blade mechanism of FIG. 2 offers greater digging resistance due to its reduction in the blade cutting angle so that a greater pushing or towing force must be provided by the tractor on which the blade is mounted. The oppositely inclined material holding angle .beta.' will cause the material being removed by the blade to drop before reaching the tip of the upper blade. Therefore, the aforesaid cutting angle and material holding angle are not preferable from the viewpoint of the efficient utilization of the tractive force of the tractor and bulldozing efficiency.
To cope with these problems, there may be proposed an attempt in which the configuration of the phantom trapezoid shape of the diagram of FIG. 3B is brought closer to that of the diagram of FIG. 3A by improving the relationship between the pins 3' and 7', the pins 1' and 7' or by changing the stroke of the piston rod of the cylinder 5', for achieving the desired cutting angle. However, the results in a further inverse inclination of the material holding angle so that the pin 1' connecting the upper blade to the push arm 4' should be positioned at the uppermost end of the upper blade or thereabove, while the position of the pin 2' relative to the pin 1' should be raised further upwards. As a result, even if the length of the arm for mounting the cylinder 5' at pin 2' is extended longer, there may not be achieved a desired configuration of the blades which are well adapted for the practical application.
In addition, there is another disadvantage, in that since the upper and lower blades are hinged by the hinge pin 7' and the upper blade is connected to the piston rod of the cylinder, the digging loads will be transmitted by way of the lower blade, pin 7', the upper blade, and the cylinder 5' to the push frame so that reasonable rigidity will be required for such members. In this respect, the arrangement of FIG. 1 is superior to that of FIG. 2 in that the loads thereof are transmitted solely by way of the lower blade and the cylinder 5, thus bypassing the hinge pin 7 and the upper blade.